Fuel cell with encapsulated electrodes

ABSTRACT

A fuel cell utilizing parallel flow of a hydrogen stream, an oxygen stream, and an electrolyte solution with respect to the electrodes, while maintaining mechanical support within the fuel cell. The fuel cell utilizes encapsulated electrodes to maintain a high air flow rate and low pressure throughout the fuel cell. The fuel cell is also designed to maintain mechanical support within the fuel cell while the electrodes expand and contract in response to the absorption of oxygen and hydrogen. Gas is predistributed by the compression plates and electrode plates to supply the electrodes with high concentrations of oxygen from air.

REFERENCE TO RELATED APPLICATIONS

The present invention is a continuation-in-part of co-pending U.S.patent application Ser. No. 10/134,756 entitled “Fuel Cell With FramedElectrodes”, filed Apr. 29, 2002 the disclosure of which is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to fuel cells. Moreparticularly, the present invention relates to alkaline fuel cellswherein the electrodes are encapsulated to allow high air flowthroughout the fuel cell while maintaining a low pressure within thefuel cell.

BACKGROUND OF THE INVENTION

Fuel cells use gaseous hydrogen streams, gaseous oxygen streams, andelectrolyte streams to produce power. The oxygen stream may be pureoxygen, air, or another oxygen containing mixture. Air, however, is themost abundant and attainable source of oxygen. Due to air containingonly 21% oxygen, a greater air flow rate is needed when air is used as asource of oxygen, as compared to a pure oxygen stream. As a result ofthe high flow rate of the oxygen stream, the pressure inside the fuelcell increases. The pressure increases inside fuel cells may causedesign problems for other streams entering and exiting the fuel cellbecause the pressure of the streams will need to be adjusted accordingto the pressure within the fuel cell. As such, a fuel cell allowing fora high air flow rate while maintaining a low pressure within the fuelcell is very desirable.

The present invention utilizes parallel flow of an electrolyte solutionwith respect to the electrodes. The electrodes are encapsulated betweenspecially designed electrode plates which distribute electrolytesolution and either air or hydrogen across the electrodes. This designallows the oxygen stream or the hydrogen stream to forcibly reach theelectrodes. The electrode plates encapsulating the electrodes are sealedtogether and flow channels in the electrode plates distribute air,hydrogen, and electrolyte solution across the electrodes whilemaintaining low pressure throughout the fuel cell. The present inventionprovides a compacted fuel cell design while allowing for a high air flowwhile maintaining a low pressure throughout the fuel cell.

As the world's population expands and its economy increases, theatmospheric concentrations of carbon dioxide are warming the earthcausing climate change. However, the global energy system is movingsteadily away from the carbon-rich fuels whose combustion produces theharmful gas. Experts say atmospheric levels of carbon dioxide may bedouble that of the pre-industrial era by the end of the next century,but they also say the levels would be much higher except for a trendtoward lower-carbon fuels that has been going on for more than 100years. Furthermore, fossil fuels cause pollution and are a causativefactor in the strategic military struggles between nations. Furthermore,fluctuating energy costs are a source of economic instability worldwide

In the United States, it is estimated, that the trend towardlower-carbon fuels combined with greater energy efficiency has, since1950, reduced by about half the amount of carbon spewed out for eachunit of economic production. Thus, the decarbonization of the energysystem is the single most important fact to emerge from the last 20years of analysis of the system. It had been predicted that thisevolution will produce a carbon-free energy system by the end of the21^(st) century. The present invention is another product which isessential to shortening that period to a matter of years. In the nearterm, hydrogen will be used in fuel cells for cars, trucks andindustrial plants, just as it already provides power for orbitingspacecraft. But, with the problems of storage and infrastructure solved(see U.S. application Ser. No. 09/444,810, entitled “A Hydrogen-basedEcosystem” filed on Nov. 22, 1999 for Ovshinsky, et al., which is hereinincorporated by reference and U.S. patent application Ser. No.09/435,497, entitled “High Storage Capacity Alloys Enabling aHydrogen-based Ecosystem”, filed on Nov. 6, 1999 for Ovshinsky et al.,which is herein incorporated by reference), hydrogen will also provide ageneral carbon-free fuel to cover all fuel needs.

A dramatic shift has now occurred, in which the problems of globalwarming and climate change are now acknowledged and efforts are beingmade to solve them. Therefore, it is very encouraging that some of theworld's biggest petroleum companies now state that they want to helpsolve these problems. A number of American utilities vow to find ways toreduce the harm done to the atmosphere by their power plants. DuPont,the world's biggest chemicals firm, even declared that it wouldvoluntarily reduce its emissions of greenhouse gases to 35% of theirlevel in 1990 within a decade. The automotive industry, which is asubstantial contributor to emissions of greenhouse gases and otherpollutants (despite its vehicular specific reductions in emissions), hasnow realized that change is necessary as evidenced by their electric andhybrid vehicles.

Hydrogen is the “ultimate fuel.” In fact, it is considered to be “THE”fuel for the future. Hydrogen is the most plentiful element in theuniverse (over 95%). Hydrogen can provide an inexhaustible, clean sourceof energy for our planet which can be produced by various processes.Utilizing the inventions of subject assignee, the hydrogen can be storedand transported in solid state form in trucks, trains, boats, barges,etc. (see the '810 and '497 applications).

A fuel cell is an energy-conversion device that directly converts theenergy of a supplied gas into an electric energy. Researchers have beenactively studying fuel cells to utilize the fuel cell's potential highenergy-generation efficiency. The base unit of the fuel cell is a cellhaving an oxygen electrode, a hydrogen electrode, and an appropriateelectrolyte. Fuel cells have many potential applications such assupplying power for transportation vehicles, replacing steam turbinesand power supply applications of all sorts. Despite their seemingsimplicity, many problems have prevented the widespread usage of fuelcells.

Presently most of the fuel cell R & D focus is on P.E.M. (ProtonExchange Membrane) fuel cells. The P.E.M. fuel cell suffers fromrelatively low conversion efficiency and has many other disadvantages.For instance, the electrolyte for the system is acidic. Thus, noblemetal catalysts are the only useful active materials for the electrodesof the system. Unfortunately, not only are the noble metals costly, theyare also susceptible to poisoning by many gases, and specifically carbonmonoxide (CO). Also, because of the acidic nature of the P.E.M. fuelcell, the remainder of the materials of construction of the fuel cellneed to be compatible with such an environment, which again adds to thecost thereof. The proton exchange membrane itself is quite expensive,and because of its low conductivity, inherently limits the powerperformance and operational temperature range of the P.E.M. fuel cell(the P.E.M. is nearly non-functional at low temperatures, unlike thefuel cell of the instant invention). Also, the membrane is sensitive tohigh temperatures, and begins to soften at 120° C. The membrane'sconductivity depends on water and dries out locally at highertemperatures, resulting in cell failure. Therefore, there are manydisadvantages to the P.E.M. fuel cell which make it somewhat undesirablefor commercial/consumer use.

The conventional alkaline fuel cell has some advantages over P.E.M. fuelcells in that they have higher operating efficiencies, they use lessexpensive materials of construction, and they have no need for expensivemembranes. The alkaline fuel cell also has relatively higher ionicconductivity in the electrolyte, therefore it has a much higher powercapability. Unfortunately, conventional alkaline fuel cells still sufferfrom certain disadvantages. For instance, conventional alkaline fuelcells still use expensive noble metals catalysts in both electrodes,which, as in the P.E.M. fuel cell, are susceptible to gaseouscontaminant poisoning. While the conventional alkaline fuel cell is lesssensitive to temperature than the P.E.M. fuel cell, the active materialsof conventional alkaline fuel cell electrodes become very inefficient atlow temperatures.

Fuel cells, like batteries, operate by utilizing electrochemicalreactions. Unlike a battery, in which chemical energy is stored withinthe cell, fuel cells generally are supplied with reactants from outsidethe cell. Barring failure of the electrodes, as long as the fuel,preferably hydrogen, and oxidant, typically air or oxygen, are suppliedand the reaction products are removed, the cell continues to operate.

Fuel cells offer a number of important advantages over internalcombustion engine or generator systems. These include relatively highefficiency, environmentally clean operation especially when utilizinghydrogen as a fuel, high reliability, few moving parts, and quietoperation. Fuel cells potentially are more efficient than otherconventional power sources based upon the Carnot cycle.

The major components of a typical fuel cell are the hydrogen electrodefor hydrogen oxidation and the oxygen electrode for oxygen reduction,both being positioned in a cell containing an electrolyte (such as analkaline electrolytic solution). Typically, the reactants, such ashydrogen and oxygen, are respectively fed through a porous hydrogenelectrode and oxygen electrode and brought into surface contact with theelectrolytic solution. The particular materials utilized for thehydrogen electrode and oxygen electrode are important since they mustact as efficient catalysts for the reactions taking place.

In an alkaline fuel cell, the reaction at the hydrogen electrode occursbetween the hydrogen fuel and hydroxyl ions (OH-) present in theelectrolyte, which react to form water and release electrons:H₂+2OH⁻→2H₂O+2e⁻.At the oxygen electrode, the oxygen, water, and electrons react in thepresence of the oxygen electrode catalyst to reduce the oxygen and formhydroxyl ions (OH⁻):O₂+2H₂O+4e⁻→4OH⁻.The flow of electrons is utilized to provide electrical energy for aload externally connected to the hydrogen and oxygen electrodes.

The catalyst in the hydrogen electrode of the alkaline fuel cell has tonot only split molecular hydrogen to atomic hydrogen, but also oxidizethe atomic hydrogen to release electrons. The overall reaction can beseen as (where M is the catalyst):M+H₂→2MH→M+2H⁺+2e⁻.Thus the hydrogen electrode catalyst must efficiently dissociatemolecular hydrogen into atomic hydrogen. Using conventional hydrogenelectrode material, the dissociated hydrogen atoms are transitional andthe hydrogen atoms can easily recombine to form molecular hydrogen ifthey are not used very quickly in the oxidation reaction. With thehydrogen storage electrode materials of the inventive instant startupfuel cells, the atomic hydrogen is immediately captured and stored inhydride form, and then used as needed to provide power.

In addition to being catalytically efficient on both interfaces, thecatalytic material must be resistant to corrosion in the alkalineelectrolyte environment. Without such corrosion resistance, theelectrodes would quickly lose efficiency and the cell will die.

One prior art fuel cell hydrogen electrode catalyst is platinum.Platinum, despite its good catalytic properties, is not very suitablefor wide scale commercial use as a catalyst for fuel cell hydrogenelectrodes, because of its very high cost. Also, noble metal catalystslike platinum cannot withstand contamination by impurities normallycontained in the hydrogen fuel stream. These impurities can includecarbon monoxide which may be present in hydrogen fuel.

The above contaminants can cause what is commonly referred to as a“poisoning” effect. Poisoning occurs where the catalytically activesites of the material become inactivated by poisonous species invariablycontained in the fuel cell. Once the catalytically active sites areinactivated, they are no longer available for acting as catalysts forefficient hydrogen oxidation reaction at the hydrogen electrode. Thecatalytic sites of the hydrogen electrode therefore are reduced sincethe overall number of available catalytically active sites issignificantly lowered by poisoning. In addition, the decrease incatalytic activity results in increased over-voltage at the hydrogenelectrode and hence the cell is much less efficient adding significantlyto the operating costs. Over-voltage is the difference between theactual working electrode potential and it's equilibrium value, thephysical meaning of over-voltage is the voltage required to overcome theresistance to the passage of current at the surface of the hydrogenelectrode (charge transfer resistance). The over-voltage represents anundesirable energy loss which adds to the operating costs of the fuelcell.

In related work, U.S. Pat. No. 4,623,597 (“the '597 patent”) and othersin it's lineage, the disclosure of which is hereby incorporated byreference, one of the present inventors, Stanford R. Ovshinsky,described disordered multi-component hydrogen storage materials for useas negative electrodes in electrochemical cells for the first time. Inthis patent, Ovshinsky describes how disordered materials can be tailormade (i.e., atomically engineered) to greatly increase hydrogen storageand reversibility characteristics. Such disordered materials areamorphous, microcrystalline, intermediate range order, and/orpolycrystalline (lacking long range compositional order) wherein thepolycrystalline material includes topological, compositional,translational, and positional modification and disorder. The frameworkof active materials of these disordered materials consist of a hostmatrix of one or more elements and modifiers incorporated into this hostmatrix. The modifiers enhance the disorder of the resulting materialsand thus create a greater number and spectrum of catalytically activesites and hydrogen storage sites.

The disordered electrode materials of the '597 patent were formed fromlightweight, low cost elements by any number of techniques, whichassured formation of primarily non-equilibrium metastable phasesresulting in the high energy and power densities and low cost. Theresulting low cost, high energy density disordered material allowed thebatteries to be utilized most advantageously as secondary batteries, butalso as primary batteries.

Tailoring of the local structural and chemical order of the materials ofthe '597 patent was of great importance to achieve the desiredcharacteristics. The improved characteristics of the hydrogen electrodesof the '597 patent were accomplished by manipulating the local chemicalorder and hence the local structural order by the incorporation ofselected modifier elements into a host matrix to create a desireddisordered material. Disorder permits degrees of freedom, both of typeand of number, within a material, which are unavailable in conventionalmaterials. These degrees of freedom dramatically change a materialsphysical, structural, chemical and electronic environment. Thedisordered material of the '597 patent have desired electronicconfigurations which result in a large number of active sites. Thenature and number of storage sites were designed independently from thecatalytically active sites.

Multiorbital modifiers, for example transition elements, provided agreatly increased number of storage sites due to various bondingconfigurations available, thus resulting in an increase in energydensity. The technique of modification especially providesnon-equilibrium materials having varying degrees of disorder providedunique bonding configurations, orbital overlap and hence a spectrum ofbonding sites. Due to the different degrees of orbital overlap and thedisordered structure, an insignificant amount of structuralrearrangement occurs during charge/discharge cycles or rest periodsthere between resulting in long cycle and shelf life.

The improved battery of the '597 patent included electrode materialshaving tailor-made local chemical environments which were designed toyield high electrochemical charging and discharging efficiency and highelectrical charge output. The manipulation of the local chemicalenvironment of the materials was made possible by utilization of a hostmatrix which could, in accordance with the '597 patent, be chemicallymodified with other elements to create a greatly increased density ofelectro-catalytically active sites and hydrogen storage sites.

The disordered materials of the '597 patent were designed to haveunusual electronic configurations, which resulted from the varying3-dimensional interactions of constituent atoms and their variousorbitals. The disorder came from compositional, positional andtranslational relationships of atoms. Selected elements were utilized tofurther modify the disorder by their interaction with these orbitals soas to create the desired local chemical environments.

The internal topology that was generated by these configurations alsoallowed for selective diffusion of atoms and ions. The invention thatwas described in the '597 patent made these materials ideal for thespecified use since one could independently control the type and numberof catalytically active and storage sites. All of the aforementionedproperties made not only an important quantitative difference, butqualitatively changed the materials so that unique new materials ensued.

Disorder can be of an atomic nature in the form of compositional orconfigurational disorder provided throughout the bulk of the material orin numerous regions of the material. The disorder also can be introducedby creating microscopic phases within the material which mimic thecompositional or configurational disorder at the atomic level by virtueof the relationship of one phase to another. For example, disorderedmaterials can be created by introducing microscopic regions of adifferent kind or kinds of crystalline phases, or by introducing regionsof an amorphous phase or phases, or by introducing regions of anamorphous phase or phases in addition to regions of a crystalline phaseor phases. The interfaces between these various phases can providesurfaces which are rich in local chemical environments which providenumerous desirable sites for electrochemical hydrogen storage.

These same principles can be applied within a single structural phase.For example, compositional disorder is introduced into the materialwhich can radically alter the material in a planned manner to achieveimproved and unique results, using the Ovshinsky principles of disorderon an atomic or microscopic scale.

SUMMARY OF THE INVENTION

The present invention discloses an improved fuel cell. The fuel cell ofthe present invention allows for a high oxygen stream flow rate (whichis essential when using air is used as the source of oxygen) whilemaintaining low pressure throughout the fuel cell. The cell design alsoprovides mechanical support within the fuel cell. The fuel cell containsat least one hydrogen electrode in contact with a hydrogen stream, atleast one oxygen electrode in contact with an oxygen stream, and atleast one electrolyte chamber in contact with the hydrogen electrode andthe oxygen electrode. The hydrogen stream may be composed of gaseoushydrogen and the oxygen stream may be composed of pure oxygen or airfrom the environment. An electrolyte solution, such as potassiumhydroxide, flows through the electrolyte chambers and contacts thehydrogen electrodes and the oxygen electrode. The fuel cell alsocontains multiple rubber compression plate used to direct oxygen andhydrogen to the electrodes and help maintain mechanical support in thefuel cell while allowing for expansion and contraction of theelectrodes.

The hydrogen and the oxygen electrodes are encapsulated in speciallydesigned electrode plates. The electrolyte chamber is placed between thehydrogen electrode and the oxygen electrode and the electrode plates areadhered together forming an electrode chamber. The electrode plates areconfigured to uniformly distribute the electrolyte solution between theelectrodes. The electrode plates also uniformly distribute hydrogen andoxygen to the respective electrodes. Hydrogen or oxygen flows throughholes in the outer face of the electrode plates and is evenlydistributed across the respective electrodes by a plurality of flowchannels on the inner face of the electrode plate. The holes in theouter face of the electrode may have different sizes to optimize theflow of hydrogen or oxygen across the respective electrodes. Preferablythe hydrogen and oxygen stream flow vertically across the electrodewhich is the shortest path for the hydrogen and oxygen stream.Alternatively, the hydrogen and oxygen stream may flow laterally acrossthe electrodes which is the longer path for the hydrogen and oxygenstream.

Compression plates are placed outside the frames within the fuel cell.The compression plates have a large opening which directs the hydrogenand oxygen to the holes in the electrode plates. The compression platesare also adapted to absorb expansion of the electrodes while providingmechanical support within the fuel cell. The compression plate may becomprised of rubber or another elastomeric compound capable of absorbingthe expansion of the electrodes.

The electrolyte chambers may be composed of a porous support structuredisposed between a pair of membranes. The membranes prevent excesselectrolyte solution from contacting the hydrogen electrodes and theoxygen electrode. The membranes also prevent the oxygen stream and thehydrogen stream from penetrating into the electrolyte. The poroussupport structure may be an expanded polymer sheet. The polymer may beof polyolefin or another rigid polymer. The electrolyte chambers contactan electrolyte contacting surface of the hydrogen electrodes and theoxygen electrodes. The electrolyte chamber is adapted to providemechanical support within the fuel cell and provide a pathway foruninterrupted flow of the electrolyte solution throughout the fuel cell.The electrolyte chambers allow the electrolyte solution to contact thehydrogen electrodes and the oxygen electrodes.

The hydrogen electrode may be composed of an anode active materialhaving hydrogen storage capacity. The hydrogen electrode has a hydrogencontacting surface, an electrolyte solution contacting surface, and abulk of an active anode material. The bulk of said anode active materialis disposed between the hydrogen contacting surface and the electrolytecontacting surface. The hydrogen contacting surface is adapted todissociate and adsorb gaseous hydrogen. The bulk of said anode activematerial is adapted to store said adsorbed hydrogen. The electrolytecontacting surface is adapted to react said stored hydrogen with anelectrolyte solution.

The hydrogen electrode may comprise an anode active material layer, aporous polytetrafluoroethylene (PTFE) layer, and a current collectorgrid. The anode active material layer may be composed of a mixture ofAB₅ type of alloy, AB₂ type of alloy, Raney nickel, graphite, and PTFEpowder. The anode active material layer is disposed between the currentcollector grid and the polytetrafluoroethylene layer. The anode activematerial layer may be dispersed throughout the current collector grid.Examples of current collector grids include, but are not limited to,mesh, grid, matte, expanded metal, foil, foam and plate. To reduce theohmic drop and better distribute current, the mesh may have 40 wires perinch running horizontally and 20 wires per inch running vertically. Thecurrent collector grid may be composed of a conductive metal such asnickel.

The oxygen electrode has an oxygen contacting surface, an electrolytesolution contacting surface, and a bulk of a cathode active material.The bulk of the cathode active material is disposed between the oxygencontacting surface and the electrolyte contacting surface. The oxygencontacting surface is adapted to dissociate and adsorb gaseous oxygen.The bulk of said cathode active material is adapted to store theadsorbed oxygen. The electrolyte contacting surface is adapted to reactthe stored oxygen with an electrolyte solution.

The oxygen electrode is composed of a gas diffusion layer, a catalystlayer, a polytetrafluoroethylene layer, and a current collector grid.The catalyst layer is disposed between the gas diffusion layer and thecurrent collector grid. The gas diffusion layer is disposed between thecatalyst layer and the polytetrafluoroethylene layer. Thepolytetrafluoroethylene layer is in intimate contact with the oxygenstream. The current collector grid is in intimate contact with saidelectrolyte stream. The current collector grid may be a mesh, grid,matte, expanded metal, foil, foam and plate. To reduce the ohmic dropand better distribute current, the mesh may have 40 wires per inchrunning horizontally and 20 wires per inch running vertically. Thecurrent collector may be composed of a conductive material such asnickel. The catalyst layer may be dispersed throughout the currentcollector grid. The gas diffusion layer may be composed of a mixture ofpolytetrafluoroethylene and carbon black. The catalyst layer may becomposed of a mixture of a mixture of polytetrafluoroethylene and carbonblack, additional carbon black, graphite, silver oxide, or othercatalysts. The silver oxide may contain a lithium aluminum alloy,gallium, molybdenum, or nickel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, shows the fuel cell of the present invention.

FIG. 2, shows a side view of the fuel cell of the present invention.

FIG. 3, shows a magnified cross sectional view of the fuel cell of thepresent invention as shown in FIG. 2.

FIG. 4, shows an exploded view of the fuel cell of the presentinvention.

FIG. 5, shows a detailed view of a hydrogen electrode in accordance withthe present invention.

FIG. 6, shows a detailed view of an oxygen electrode in accordance withthe present invention.

FIG. 7, shows a detailed view of the inner side of a hydrogen electrodeplate in accordance with the present invention.

FIG. 8, shows a detailed view of the outer side of a hydrogen electrodeplate in accordance with the present invention.

FIG. 9, shows a detailed view of the inner side of an oxygen electrodeplate in accordance with the present invention.

FIG. 10, shows a detailed view of the outer side of an oxygen electrodeplate in accordance with the present invention.

FIG. 11, shows a detailed view of the inner side of a hydrogen electrodeplate in accordance with the alternative embodiment of the presentinvention.

FIG. 12, shows a detailed view of the outer side of a hydrogen electrodeplate in accordance with the alternative embodiment of the presentinvention.

FIG. 13, shows a detailed view of the inner side of an oxygen electrodeplate in accordance with the alternative embodiment of the presentinvention.

FIG. 14, shows a detailed view of the outer side of an oxygen electrodeplate in accordance with the alternative embodiment of the presentinvention.

FIG. 15, shows a detailed view of a compression plate in accordance withthe present invention.

FIG. 16, shows a detailed view of a compression plate in accordance withthe alternative embodiment of the present invention.

FIG. 17, shows a detailed cross sectional view of the electrolytechamber in accordance with the present invention.

FIG. 18, shows a cross sectional view of the preferred embodiment of thehydrogen electrode in accordance with the present invention.

FIG. 19, shows a cross sectional view of the preferred embodiment of theoxygen electrode in accordance with the present invention.

FIG. 20, is an exploded view of the fuel cell of the present invention,specifically shown is the flow of hydrogen through the fuel cell.

FIG. 21, is an exploded view of the alternative embodiment of the fuelcell of the present invention, specifically shown is the flow ofhydrogen through the fuel cell.

FIG. 22, is an exploded view of the fuel cell of the present invention,specifically shown is the flow of electrolyte solution through the fuelcell.

FIG. 23, is an exploded view of the fuel cell of the present invention,specifically shown is the flow of air through the fuel cell.

FIG. 24, is an exploded view of the alternative embodiment of the fuelcell of the present invention, specifically shown is the flow of airthrough the fuel cell.

DETAILED DESCRIPTION OF THE INVENTION

In the past, fuel cells have been designed to use air as a source ofoxygen. When air is used as an oxygen source, the air flow rate must beapproximately 5 times the required flow rate of pure oxygen, due to aircontaining 21% oxygen. The high air flow rate can substantially raisethe pressure within the fuel cell thereby creating design problems. Thepresent invention allows for a high air flow rate while maintaining alow pressure throughout the fuel cell. This invention applies parallelflow of a hydrogen stream, an oxygen stream, and an electrolyte streamthroughout a fuel cell with respect to framed electrodes. The componentsof the fuel cell are compacted tightly together to provide mechanicalsupport throughout the fuel cell while allowing for electrode expansion.While the fuel cell may be compacted together, the fuel cell allowsuninterrupted flow of hydrogen, oxygen, and an electrolyte solutionacross the electrodes. Gases and liquids flow through the cell via flowchannels and porous structures. The design of the present inventionallows for high speed gas flow throughout the fuel cell whilemaintaining a low pressure throughout the cell. The fuel cell alsoallows for expansion of the electrodes by using layers designed toabsorb the expansion of the electrodes in the Z direction as theelectrodes absorb hydrogen.

The fuel cell 10 of the present invention is shown in FIG. 1. The layersof the fuel cell have multiple holes through which oxygen, hydrogen, andelectrolyte solution flow. When the layers are stacked and pressedtogether, the holes of each layer line up to allow uninterrupted flowthroughout the cell. The fuel cell has a hydrogen inlet 11, an oxygeninlet 12, two electrolyte inlets 13, a hydrogen outlet 14, a oxygenoutlet 15, and two electrolyte outlets 16. The hydrogen flows into thefuel cell through the hydrogen inlet 11 to the hydrogen electrode. Thehydrogen is distributed across the hydrogen contacting side of thehydrogen electrode and is absorbed by the hydrogen electrode with theexcess hydrogen flowing out of the fuel cell through the hydrogen outlet14. The excess hydrogen may be used to help remove heat generated by theabsorption of hydrogen from the fuel cell. Oxygen or an oxygencontaining mixture, such as air, flows into the fuel cell through theoxygen inlet 12 to the oxygen electrode. The oxygen stream isdistributed across the oxygen contacting side of the oxygen electrodeand is adsorbed by the oxygen electrode. The remaining oxygen streamcontaining unconsumed oxygen and nitrogen then flows out of the fuelcell through the oxygen outlet 15. An oxygen outlet 15 may not be neededwhen a pure oxygen stream is used as the oxygen source, where the systemis configured to consume all oxygen input into the fuel cell. When airis used as the oxygen source, the air flows across the oxygen electrodeand the oxygen is absorbed from the air. The remaining nitrogen andcarbon dioxide left from the air stream flow out of the fuel cellthrough the oxygen outlet. The remaining air stream may also help removeheat from the fuel cell. The electrolyte solution flows into the fuelcell through the electrolyte inlets to the electrolyte chamber.

The electrolyte solution is distributed through the electrolyte chamberand contacts the hydrogen and oxygen electrodes. The electrolytesolution preferably flows across the shorter side of the electrodes.After the electrolyte solution flows past the electrodes, theelectrolyte solution then flows out of the fuel cell through theelectrolyte outlets 16. The exiting electrolyte solution may also helpremove heat from the fuel cell.

A side view of the fuel cell is shown in FIG. 2. A cross-sectional viewof the fuel cell of FIG. 2 is shown in FIG. 3 and an exploded view ofthe fuel cell of FIG. 2 is shown in FIG. 4. The fuel cell has a stackformation with multiple layers. The fuel cell contains at least onehydrogen electrode 20 and at least one electrode 40. The hydrogenelectrode 20 and oxygen electrode 40 are each disposed in electrodeplates. An electrolyte chamber 60 is placed in between the hydrogenelectrode 20 and the oxygen electrode 40. The hydrogen electrode plate30 and the oxygen electrode plate 50 are adhered together to form anelectrode chamber containing the hydrogen electrode 20, the oxygenelectrode 40, and the electrolyte chamber 60. The hydrogen electrodeplate 30 and the oxygen electrode plate 50 can be adhered together usingepoxy, plastic welding, or other modes of hermetic sealing. Rubbercompression plates 70 are placed outside the hydrogen electrode plate 30and the oxygen electrode plate 50, and electrode end plates 80 areplaced outside the rubber compression plates 70 to complete the stack.The electrode end plates 80 are bolted together and provide mechanicalsupport and compression to the fuel cell.

The fuel cell is easily expandable by addition of electrode chambers asdictated by design requirements. In such case additional hydrogenelectrodes, oxygen electrodes, and electrolyte chambers, electrodeplates, and compression plates may be added. The layers may bepositioned as earlier described with two hydrogen electrodes sharing thehydrogen stream and two oxygen electrodes sharing the oxygen stream.

Each fuel cell contains at least one hydrogen electrode 20. A moredetailed view of an hydrogen electrode in accordance with the presentinvention is shown in FIG. 5. The hydrogen electrode is substantiallyrectangular in shape. An aspect ratio of 1 to 1 for the hydrogenelectrode is preferred to better accommodate electrode expansion,current distribution, and current collection, however, other aspectratios may be used in accordance with the present invention. Thehydrogen electrode may be composed of a hydrogen storage alloy. Thehydrogen electrode is flat with a current collector 21 running along oneof the longer sides of the hydrogen electrode 20. The current collector21 is also electrically connected to the hydrogen electrode 20.

Each fuel cell also contains at least one oxygen electrode 40. A moredetailed view of an oxygen electrode in accordance with the presentinvention is shown in FIG. 6. The oxygen electrode is substantiallyrectangular in shape. An aspect ratio of 1 to 1 for the hydrogenelectrode is preferred optimize current distribution and currentcollection, however, other aspect ratios may be used in accordance withthe present invention. The oxygen electrode is flat with a currentcollector 41 running along one of the longer sides of the oxygenelectrode 40. The current collector 41 is also electrically connected tothe oxygen electrode 40.

The hydrogen electrode 20 is placed in a hydrogen electrode plate 30 andthe oxygen electrode 40 is placed in an oxygen electrode plate 50. Eachplate has an inner side and an outer side. A detailed view of thehydrogen electrode plate can be seen in FIG. 7 and FIG. 8. A detailedview of the oxygen electrode plate can be seen in FIG. 9 and FIG. 10.The inner side 31 of the hydrogen electrode plate 30 has a depression 32into which the hydrogen electrode 20 fits and the inner side 51 of theoxygen electrode plate 50 has a depression 52 into which the oxygenelectrode 40 fits. The depression 32 in the hydrogen electrode plate 30and the depression 52 in the oxygen electrode plate 50 are slightlylarger than the electrodes thereby allowing for expansion of theelectrodes. A plurality of hydrogen flow channels 33 extend across theface of the depression in the inner side 31 of the hydrogen electrodeplate 30 and a plurality of oxygen flow channels 53 extend across theface of the depression 52 in the inner side 51 of the oxygen electrodeplate 50. The hydrogen electrode plate has a plurality of holes 34through which hydrogen flows from the outer side 37 of the hydrogenelectrode plate to the inner side 31 of the hydrogen electrode plate,thus flowing through the hydrogen flow channels 33 on the inner side 31of the hydrogen electrode plate 30 and contacting the hydrogen electrode20. The oxygen electrode plate 50 has a plurality of holes 54 throughwhich the oxygen stream flows from the outer side 57 of the oxygenelectrode plate to the inner side 51 of the oxygen electrode plate, thusflowing through the oxygen flow channels 53 on the inner side 51 of theoxygen electrode plate 50 and contacting the oxygen electrode 40. Theholes in the hydrogen electrode plate and the holes in the oxygenelectrode plate may have different sizes to optimize flow of thehydrogen stream or the oxygen stream across the respective electrodes.Preferably, the holes are configured to allow the hydrogen and oxygenstream to flow vertically across the hydrogen electrode and the oxygenelectrode. This allows the hydrogen stream and oxygen stream to have ashorter path across the electrodes thus optimizing performance of thefuel cell. The electrode plates may also be configured to allow thehydrogen stream and the oxygen stream to flow laterally across theelectrodes. This design is utilized in an alternative embodiment 10A ofthe fuel cell of the present invention. The alternative embodiment ofthe hydrogen electrode plate 30A is shown in FIG. 11 and FIG. 12. Thealternative embodiment of the oxygen electrode plate 50A is shown inFIG. 13 and FIG. 14. Same reference numbers refer to the same elementsin the different embodiments.

Once the hydrogen electrode 20 and the oxygen electrode 40 are placed intheir respective plates, an electrolyte chamber 60 is placed between thehydrogen electrode 20 and the oxygen electrode 40 and the plates areadhered together to form an electrode chamber. The inner side 31 of thehydrogen electrode plate 30 and the inner side 51 of the oxygenelectrode plate 50 have flow distributing structures 35 located withinelectrolyte flow channels 36 which evenly distribute the electrolytesolution through the electrolyte chamber when the hydrogen electrodeplate 30 and the oxygen electrode plate 50 are adhered together, therebyeliminating the need for manifolds while maintaining low pressurethroughout the fuel cell. The flow distributing structures 35 may alsoprovide mechanical support to the fuel cell. The flow distributingstructures 35 are located where the electrolyte solution enters theelectrode chamber. The flow distributing structures 35 preferably have atriangular shape, however circular or other polygonal shapes may be usedin accordance with the present invention. The hydrogen electrode plate30 and the oxygen electrode plate 50 together form the flow distributingstructures 35. One half of the flow distributing structures 35 protrudefrom each plate and when the plates are pressed together the halves lineup and form the flow distributing structures 35. The flow distributingstructures 35 extend from the hydrogen electrode plate 30 to the oxygenelectrode plate 50 and force the electrolyte solution flowing throughthe electrolyte flow channels to flow around them, thereby evenlydistributing the electrolyte solution between the hydrogen electrode 20and oxygen electrode 40.

The outer side 37 of the hydrogen electrode plate 30 has a depression 38into which a rubber compression plate 70 fits and the outer side 57 ofthe oxygen electrode plate 50 has a depression 58 into which a secondcompression plate 70 fits. The thickness of the compression plate 70 maybe greater than the depth of the depression in the outer side of thehydrogen electrode plate 37 and the depression in the outer side of theoxygen electrode plate 57 to provide mechanical support and propersealing within the fuel cell 10.

The hydrogen electrode plate and the oxygen electrode plate aresubstantially similar, however, the hydrogen electrode plate 30 has atongue 39 along its edge which fits into a groove 59 along the edge ofthe oxygen electrode plate 50. This tongue and groove design allows forproper assembly of the fuel cell and provides an area for epoxy oranother adhering substance to be placed for securing the two plates.

Compression plates 70 are inserted into the fuel cell to absorbvolumetric expansion of the electrodes, distribute hydrogen and oxygenacross the respective electrodes, and help maintain mechanical supportof the fuel cell stack. A detailed view of a rubber compression plate inaccordance with the present invention is shown in FIG. 15. A detailedview of compression plate 70A in accordance with the alternativeembodiment of the present invention implementing lateral flow of thehydrogen stream and the oxygen stream across the electrodes is shown inFIG. 16. The compression plates are placed in contact with the outersides of the hydrogen electrode plate and the oxygen electrode plate.The compression plates 70 have cutout sections 71 which direct thehydrogen stream to a plurality of holes 34 in the hydrogen electrodeplate and direct the oxygen steam to a plurality of holes 54 in theoxygen electrode plate. The compression plates are located between theelectrode end plates 80 and the electrode plates. The compression platesare also designed to absorb expansion of the electrodes in the Zdirection as the electrodes expand and contract as hydrogen and oxygenare absorbed and reacted by the respective electrodes. The compressionplates may be constructed from any rubber type material, however therubber material must not be reactive with the alkaline electrolytesolution and must be able to withstand the operating temperatures of thefuel cell.

Electrolyte chambers may be used to maintain mechanical support withinthe fuel cell while creating an electrolyte chamber which allows theelectrolyte solution to flow throughout the fuel cell. A more detailedview of an electrolyte chamber in accordance with the present inventionis shown in FIG. 17. The electrolyte chambers 60 may be composed of anexpanded polyolefin sheet having a thin membrane on each side. Themembrane helps prevent excess electrolyte from contacting the electrodeand also prevents hydrogen or oxygen from penetrating into theelectrolyte solution. The electrolyte chamber 60 may be placed betweenthe hydrogen electrode 20 and the oxygen electrode 40 in the fuel cell.The electrolyte chamber may be in direct contact with the electrodes.While the electrolyte chamber is preferably constructed from an expandedpolyolefin sheet, any porous material that allows unrestricted flowthroughout its structure while maintaining mechanical support of thefuel cell may be substituted. The porous material must also be one thatdoes not react with the alkaline electrolyte solution and must be ableto withstand the operating temperatures of the fuel cell. Inside theelectrolyte chamber, the electrolyte solution contacts the hydrogenelectrode 20 and the oxygen electrode 40. The electrolyte solutionenters the fuel cell and flows through the electrolyte chamber 60. Afterpassing through the electrolyte chamber, the electrolyte solution flowsout of the fuel cell.

The hydrogen electrode may be generally composed of an anode activematerial having hydrogen storage capacity. The anode active material isdesigned to have a high density of active catalytic sites, resistance topoisoning, and long operating life to provide efficient low cost fuelcell operation.

An anode active material of the instant invention may be a composite ofa hydrogen storage material and an additional catalytic material. Thepreferable anode active material is one which can reversibly absorb andrelease hydrogen irrespective of the hydrogen storage capacity and hasthe properties of a fast hydrogenation reaction rate, a good stabilityin the electrolyte and a long shelf-life. It should be noted that, byhydrogen storage capacity, it is meant that the material stores hydrogenin a stable form, in some nonzero amount higher than trace amounts.Preferred materials will store about 0.1 weight % hydrogen or more.Preferably, the alloys include, for example, rare-earth/Misch metalalloys, zirconium and/or titanium alloys or mixtures thereof. Thehydrogen electrode material may even be layered such that the materialon the hydrogen contacting surface is formed from a material which hasbeen specifically designed to be highly catalytic to the dissociation ofmolecular hydrogen into atomic hydrogen, while the material onelectrolyte contacting surface is designed to be highly catalytic to theelectrochemical oxidation of hydrogen.

Certain hydrogen storage materials are exceptionally useful as alkalinefuel cell hydrogen electrode materials. The useful hydrogen storagealloys have excellent catalytic activity for the formation of hydrogenatoms from molecular hydrogen and also have superior catalytic activitytoward the electrochemical oxidation of hydrogen atoms. In addition tohaving exceptional catalytic capabilities, the materials also haveoutstanding corrosion resistance toward the alkaline electrolyte of thefuel cell. In use, the alloy materials act as 1) a molecular hydrogendecomposition catalyst throughout the bulk of the hydrogen electrode;and 2) as an internal hydrogen storage buffer to insure that a readysupply of hydrogen atoms is always available at the electrolyteinterface.

Specific alloys useful as the hydrogen electrode material are alloysthat contain enriched catalytic nickel regions of 50-70 Angstroms indiameter distributed throughout the oxide interface which vary inproximity from 2-300 Angstroms preferably 50-100 Angstroms, from regionto region. As a result of these nickel regions, the materials exhibitsignificant catalysis and conductivity. The density of Ni regions in thealloys provide powder particles having an enriched Ni surface. The mostpreferred alloys having enriched Ni regions are alloys having thefollowing composition:(Base Alloy)_(a)Co_(b)Mn_(c)Fe_(d)Sn_(e)where the Base Alloy comprises 0.1 to 60 atomic percent Ti, 0.1 to 40atomic percent Zr, 0 to 60 atomic percent V, 0.1 to 57 atomic percentNi, and 0 to 56 atomic percent Cr; b is 0 to 7.5 atomic percent; c is 13to 17 atomic percent; d is 0 to 3.5 atomic percent; e is 0 to 1.5 atomicpercent; and a+b+c+d+e=100 atomic percent. Such materials are disclosedin U.S. Pat. No. 5,536,591 to Fetcenko et al., published Jul. 16, 1996,the disclosure of which is hereby incorporated by reference.

The hydrogen electrode 20 in the preferred embodiment of the presentinvention has a layered structure and is shown in FIG. 18. The layeredstructure promotes hydrogen dissociation and absorption within thehydrogen electrode 20. Each hydrogen electrode is composed of an activematerial layer 22, a current collector grid 23, and a porouspolytetrafluoroethylene layer 24. The active material layer 22 isdisposed between the current collector grid 23 and thepolytetrafluoroethylene layer 24. The active material layer 22 may bedispersed throughout the current collector grid 23. Examples of currentcollector grids include, but are not limited to, mesh, grid, matte,expanded metal, foil, foam and plate. The preferable current collectorgrid is a conductive mesh having 40 wires per inch horizontally and 20wires per inch vertically. The wires comprising the mesh may have adiameter between 0.005 inches and 0.01 inches, preferably between 0.005inches and 0.008 inches. This design provides optimal currentdistribution due to the reduction of the ohmic resistance. Where morethan 20 wires per inch are vertically positioned, problems may beencountered when affixing the active material to the substrate. Thecurrent collector grid may be composed of a conductive material such asnickel. Other conductive materials may be substituted as required bydesign constraints. The polytetrafluoroethylene layer 24 may beapproximately 0.0007 inches thick. The current collector grid 23 is onthe electrolyte contacting side of the hydrogen electrode 20 and thepolytetrafluoroethylene layer 24 is on the hydrogen contacting side ofthe hydrogen electrode 20.

The active material layer 22 may be composed of Misch metal nickelalloy, Raney nickel, graphite, and polytetrafluoroethylene powder. Apreferred composition of the active material layer 23 is by weight 35%Mischmetal nickel alloy, 46% Raney nickel, 4% graphite, and 15%polytetrafluoroethylene. The most preferred Misch metal nickel alloy hasthe following composition by weight percent:

50.07% Ni, 10.62% Co, 4.6% Mn, 1.8% Al, 20.92% La, 8.63% Ce, 0.87% Pr,and 2.49% Nd. The graphite may be one with isotropic shape having highelectrical and thermal conductivity. A typical example of such graphiteis called TIMREX KS-75 (Trademark of Timcal Group). Raney nickel andpolytetrafluoroethylene are well known in the art and do not need anyfurther discussion.

The oxygen electrode may contain an active material component which iscatalytic to the dissociation of molecular oxygen into atomic oxygen,catalytic to the formation of hydroxyl ions (OH⁻) from water and oxygenions, corrosion resistant to the electrolyte, and resistant topoisoning. A material useful as an active material in the oxygenelectrode is on a host matrix including at least one transition metalelement which is structurally modified by the incorporation of at leastone modifier element to enhance its catalytic properties. Such materialsare disclosed in U.S. Pat. No. 4,430,391 ('391) to Ovshinsky, et al.,published Feb. 7, 1984, the disclosure of which is hereby incorporatedby reference. Such a catalytic body is based on a disorderednon-equilibrium material designed to have a high density ofcatalytically active sites, resistance to poisoning and long operatinglife. Modifier elements, such as La, Al, K, Cs, Na, Li, Ga, C, and Ostructurally modify the local chemical environments of the host matrixincluding one or more transition elements such as Mn, Co and Ni to formthe catalytic materials of the oxygen electrode. These low over-voltage,catalytic materials increase operating efficiencies of the fuel cells inwhich they are employed.

The oxygen electrode may be formed the same as conventional oxygenelectrodes which use platinum catalysts, but the non-noble-metalcatalysts described above are substituted for the platinum. Thenon-noble catalysts are finely divided and disbursed throughout a porouscarbon matte-like material. The material may or may not have aconductive substrate as needed.

The fuel cell oxygen electrodes of this invention may also utilize redoxcouples, particularly metal/oxides couples selected from the group ofmetals consisting of copper, silver, zinc, cobalt and cadmium. Thesetypes of oxygen electrodes are discussed in detail in the commonly ownedcopending application Ser. No. 90/737,332, the disclosure of which ishereby incorporated by reference.

The oxygen electrodes of the instant invention may also include acatalytic material which promotes and speeds the dissociation ofmolecular oxygen into atomic oxygen (which reacts with the redoxcouple). A particularly useful catalyst is carbon. This carbon should bevery porous and may be electrically conductive.

The oxygen electrode also needs a barrier means to isolate theelectrolyte, or wet, side of the oxygen electrode from the gaseous, ordry, side of the oxygen electrode. A beneficial means of accomplishingthis is by inclusion of a hydrophobic component comprising a halogenatedorganic compound, particularly polytetrafluoroethylene (PTFE) within theelectrode.

The oxygen electrodes, may also include a current collector grid orcurrent collecting system extending within said active material. Thecurrent collector may comprise an electrically conductive mesh, grid,foam or expanded metal. The most preferable current collector grid is aconductive mesh having 40 wires per inch horizontally and 20 wires perinch vertically. The wires comprising the mesh may have a diameterbetween 0.005 inches and 0.01 inches, preferably between 0.005 inchesand 0.008 inches. This design provides optimal current distribution dueto the reduction of the ohmic resistance. Where more than 20 wires perinch are vertically positioned, problems may be encountered whenaffixing the active material to the substrate.

The oxygen electrodes in the preferred embodiment of the presentinvention have a layered structure and are shown in FIG. 19. The layeredstructure promotes oxygen dissociation and absorption within the oxygenelectrode 40. Each oxygen electrode 40 is composed of an A layer 42, a Blayer 43, a current collector grid 44, and a polytetrafluoroethylenelayer 45. The A layer 42 may be composed of carbon particles coated withpolytetrafluoroethylene. The carbon particles may be carbon black knownas Vulcan XC-72 carbon (Trademark of Cabot Corp.), which is well knownin the art. The A layer 42 may contain approximately 40 percent byweight polytetrafluoroethylene with the remainder consisting of carbonparticles. The B layer may be composed of the A layer material andadditional carbon particles, graphite and silver oxide. The B layer 43may contain approximately 50 percent of the material of the A layer, 15percent carbon, 15 percent graphite and 20 percent silver oxide. Thecarbon added to the B layer 43 is carbon black known as Black Pearl 2000(Trademark of Cabot Corp.). The graphite is preferably TIMREX SFG 44graphite (Trademark of Timcal Group). The silver oxide may also containa lithium-aluminum alloy, gallium, or other modifiers for improvedperformance.

Reactive elements such as lithium may be added to the redox couple inthe form of a non-reactive alloy such as a LiAl alloy. That is, lithiumalone as an individual element is extremely reactive with oxygen andwater vapor, therefore it is advisable to incorporate the element intothe redox couple in the form of an alloy with aluminum which is notreactive in this way. Other elements which may be alloyed with thelithium include boron and silicon. Specifically the LiAl alloy is a50:50 At. % alloy. Ga may also be added to the silver oxide. Specificexamples of silver oxides containing an Li—Al alloy or Ga are shown inTable 1. Such materials are disclosed in commonly owned copendingapplication Ser. No. 09/797,332, filed Mar. 1, 2001, the disclosure ofwhich is hereby incorporated by reference. TABLE 1 Analysis (TCP for1-6; Sample Description EDS rest)  5% LiAl, 95% Ag from Li:0.006%,Al:0.07%, nitrates Ag:99.924%  1% LiAl, 99% Ag from Li:0.001, Ag 99.999%alloy 10% LiAl, 90% Ag from Li:0.82%, Al:5.16%, alloy Ag:94.02 5% LiAl,95 % Ag from Li:0.034%, Al:0.29%, alloy Ag:99.676% LiAl, Ag Ag:100% 1%Ga, 99% Ag Ag:100% 5% Ga, 95% Ag Ga:0.7%, Ag:99.3%

The current collector grid 44 is placed on top of the B layer 43 whichis placed on top of the A layer 42. The B layer 43 may be dispersedthroughout the current collector grid 44. Examples of current collectorgrids include, but are not limited to, mesh, grid, matte, expandedmetal, foil, foam and plate. The current collector grid may be composedof a conductive material such as nickel. Other conductive materials maybe substituted as required by design constraints. The other side of theA layer 42 is coated with a film of polytetrafluoroethylene 45. Thenickel wire mesh is in contact with the electrolyte solution and thepolytetrafluoroethylene layer is in contact with the oxygen stream.

The flow of hydrogen through the fuel cell is shown in FIG. 20. Hydrogenenters the fuel cell 10 through the hydrogen inlet 11 and flows to theouter side of the hydrogen electrode frame 30. The hydrogen is thendistributed through the hydrogen electrode frame 30 and across thehydrogen contacting side 26 of the hydrogen electrode 20 through flowchannels formed in the compression plate 70 in contact with the outerside of the hydrogen electrode frame 33. Hydrogen is absorbed throughthe hydrogen contacting surface 26 into the hydrogen electrode 20. Theabsorbed hydrogen is catalytically broken down by the anode activematerial into atomic hydrogen which is stored in the hydrogen storagematerial as a hydride. The stored atomic hydrogen then finally reacts atthe electrolyte contacting surface 27 with hydroxyl ions to form water.It should be noted that the heat of hydride formation may help to warmthe fuel cell to it's optimal operating temperature. Any unabsorbedhydrogen and other contaminant gases or water vapor in the hydrogensupply are vented through the hydrogen outlet 14. The vented gases maybe recycled if enough hydrogen is present to warrant recovery. Otherwisethe hydrogen may be used to provide a source of thermal energy if neededfor other components such as a hydride bed hydrogen storage tank. Theflow of hydrogen through the alternate embodiment of the fuel cell 10Ais shown in FIG. 21.

The flow of the electrolyte solution through the fuel cell is shown inFIG. 22. The electrolyte solution is an aqueous alkaline electrolyte inintimate contact with the electrolyte contacting surfaces of hydrogenelectrodes and the oxygen electrodes. The alkaline solution is wellknown in the art and is typically a potassium hydroxide solution. Theelectrolyte solution is supplied to the porous electrolyte chambersthrough electrolyte solution inlets 13. The electrolyte solution isdistributed through the electrolyte chamber 60 by flow distributingstructures located in the oxygen and hydrogen electrode frame 30 and theoxygen electrode frame 50. The electrolyte solution flows through theelectrolyte chamber 60 and contacts the electrolyte contacting surfaceof the hydrogen electrode 27 and the electrolyte contacting surface ofthe oxygen electrode 47. The electrolyte provides hydroxyl ions whichreact with hydrogen ions at the electrolyte contacting surface of thehydrogen electrode and water molecules which react with oxygen ions atthe electrolyte contacting surface of the oxygen electrode. Theelectrolyte is circulated through the fuel cell via inlets 13 andoutlets 16 (in alternative embodiments, the electrolyte may bedeliberately immobilized as by jelling, etc.) The circulated electrolytemay be externally heated or cooled as necessary, and the concentrationof the electrolyte can be adjusted as needed to compensate for the waterproduced by the cell and any losses due to evaporation of water throughthe electrodes. Systems for conditioning the fuel cell electrolyte arewell known in the art and need not be further described in detailherein.

The flow of oxygen through the fuel cell is shown in FIG. 23. Oxygenenters the fuel cell through the oxygen inlet and flows to the outerside of the oxygen electrode plate 50. The oxygen is then distributedthrough the oxygen electrode frame 50 and across the oxygen contactingside 46 of the oxygen electrode 40 by flow channels formed in thecompression plate 70 in contact with the outer side of the oxygenelectrode frame 50. Oxygen is then adsorbed through the oxygencontacting surface 46 into the oxygen electrode 40. The adsorbed oxygenis catalytically broken down by the cathode active material. Thereactive oxygen is then electrochemically reduced at the electrolyteinterface to form hydroxyl ions. Any unadsorbed oxygen and other gasesin the feed (e.g. nitrogen, carbon dioxide, etc.) or water vapor in theoxygen supply are vented through the oxygen outlet 15. The flow ofoxygen through the alternate embodiment of the fuel cell 10A is shown inFIG. 24.

The foregoing is provided for purposes of explaining and disclosingpreferred embodiments of the present invention. Modifications andadaptations to the described embodiments, particularly involving changesto the shape of the fuel cell, the type of hydrogen storage alloy, thecathode active material, the shape and design of the electrodes withinthe fuel cell, and the shape and design of the electrode flow channels,will be apparent to those skilled in the art. These changes and othersmay be made without departing from the scope or spirit of the inventionin the following claims.

1. A fuel cell comprising: at least one hydrogen electrode plate havingan inner side and an outer side, wherein a hydrogen electrode isdisposed within said inner side of said hydrogen electrode plate and acompression plate is disposed within said outer side of said hydrogenelectrode plate; at least one oxygen electrode plate having an innerside and an outer side, wherein an oxygen electrode is disposed withinsaid inner side of said oxygen electrode plate and a compression plateis disposed within said outer side of said oxygen electrode plate; atleast one electrolyte chamber disposed between said hydrogen electrodeand said oxygen electrode; said compression plate which is disposedwithin said hydrogen electrode plate is configured to direct a hydrogenstream which is in contact with said outer side of said hydrogenelectrode plate through at least one hole in said hydrogen electrodeplate to a series of hydrogen flow channels within said inner side ofsaid hydrogen electrode plate, said hydrogen flow channels configured todistribute said hydrogen stream across said hydrogen electrode; saidcompression plate which is disposed within said oxygen electrode plateis configured to direct an oxygen containing stream which is in contactwith said outer side of said oxygen electrode plate through at least onehole in said oxygen electrode plate to a series of oxygen flow channelswithin said inner side of said oxygen electrode plate, said oxygen flowchannels configured to distribute said oxygen containing stream acrosssaid oxygen electrode; said inner sides of said hydrogen electrode plateand said oxygen electrode plate being adhered together forming a seriesof electrolyte flow channels disposed between said hydrogen electrodeplate and said oxygen electrode plate, and a plurality of electrolyteflow distributing structures disposed within said electrolyte flowchannels, said series of electrolyte flow channels and said electrolyteflow distributing structures being configured to uniformly distribute anelectrolyte solution laterally through said electrolyte chamber.
 2. Thefuel cell according to claim 1, wherein said hydrogen electrode plateand said oxygen electrode plate have a tongue and groove configuration.3. The fuel cell according to claim 1, wherein said flow distributingstructures extend from said hydrogen electrode plate to said oxygenelectrode plate.
 4. The fuel cell according to claim 1, wherein saidflow distributing structures provide support to said fuel cell.
 5. Thefuel cell according to claim 1, wherein said flow distributingstructures have a polygonal cross section.
 6. The fuel cell according toclaim 1, wherein said flow distributing structures have a circular crosssection.
 7. The fuel cell according to claim 1, wherein said electrolytechamber provides mechanical support within said fuel cell and provides apathway for said electrolyte solution to contact said hydrogen electrodeand said oxygen electrode.
 8. The fuel cell according to claim 1,wherein said electrolyte chamber contacts an electrolyte contactingsurface of said hydrogen electrode and said oxygen electrode.
 9. Thefuel cell according to claim 1, wherein said electrolyte chamber furthercomprises a porous support structure disposed between a pair ofmembranes.
 10. The fuel cell according to claim 9, wherein said pair ofmembranes prevent excess electrolyte solution from contacting saidhydrogen electrode and said oxygen electrode.
 11. The fuel cellaccording to claim 9, wherein said pair of membranes prevent said oxygencontaining stream and said hydrogen stream from penetrating into saidelectrolyte.
 12. The fuel cell according to claim 9, wherein said poroussupport structure is comprised of an expanded polymer sheet.
 13. Thefuel cell according to claim 12, wherein said expanded polymer sheet iscomprised of a polyolefin.
 14. The fuel cell according to claim 1,wherein said compression plates are adapted to absorb expansion of saidhydrogen electrode.
 15. The fuel cell according to claim 1, wherein saidcompression plates provide mechanical support within said fuel cell. 16.The fuel cell according to claim 1, wherein said compression plates arecomprised of rubber.
 17. (CANCELED)
 18. The fuel cell according to claim1, wherein said hydrogen electrode comprises an anode active materialhaving hydrogen storage capacity.
 19. (CANCELED)
 20. The fuel cellaccording to claim 18, wherein said hydrogen electrode has a hydrogencontacting surface, an electrolyte solution contacting surface, and abulk of said active anode material.
 21. The fuel cell according to claim20, wherein said bulk of said anode active material is disposed betweensaid hydrogen contacting surface and said electrolyte contactingsurface.
 22. The fuel cell according to claim 20, wherein said hydrogencontacting surface is adapted to dissociate and absorb gaseous hydrogen.23. The fuel cell according to claim 22, wherein said bulk of said anodeactive material is adapted to store said absorbed hydrogen.
 24. The fuelcell according to claim 20 23, wherein said electrolyte solutioncontacting surface is adapted to react said stored hydrogen with anelectrolyte solution.
 25. The fuel cell according to claim 1, whereinsaid hydrogen electrode comprises an anode active material layer, aporous polytetrafluoroethylene layer, and a current collector grid. 26.The fuel cell according to claim 25, wherein said anode active materiallayer is disposed between said current collector grid and saidpolytetrafluoroethylene layer.
 27. The fuel cell according to claim 25,wherein said anode active material layer is dispersed throughout saidcurrent collector grid.
 28. The fuel cell according to claim 25, whereinsaid anode active material layer comprises a mixture of mischmetalnickel alloy, raney nickel, graphite, and polytetrafluoroethylenepowder.
 29. The fuel cell according to claim 28, wherein said anodeactive material layer has the following composition: 35 weight percentmischmetal nickel alloy, 46 weight percent raney nickel, 4 weightpercent graphite, and 15 weight percent polytetrafluoroethylene powder.30. The fuel cell according to claim 25, wherein said current collectorgrid comprises at least one selected from the group consisting of mesh,grid, matte, expanded metal, foil, foam and plate.
 31. The fuel cellaccording to claim 25, wherein said current collector grid comprises 40wires per inch running horizontally and 20 wires per inch runningvertically.
 32. The fuel cell according to claim 25, wherein saidcurrent collector grid is comprised of a conductive metal.
 33. The fuelcell according to claim 32, wherein said conductive metal is nickel. 34.(CANCELED)
 35. The fuel cell according to claim 1, wherein said oxygenelectrode comprises a cathode active material.
 36. (CANCELED)
 37. Thefuel cell according to claim 35, wherein oxygen electrode has an oxygencontacting surface, an electrolyte solution contacting surface, and abulk of said cathode active material.
 38. The fuel cell according toclaim 37, wherein said bulk of said cathode active material is disposedbetween said oxygen contacting surface and said electrolyte solutioncontacting surface.
 39. The fuel cell according to claim 37, whereinsaid oxygen contacting surface is adapted to dissociate and absorbgaseous oxygen.
 40. The fuel cell according to claim 39, wherein saidbulk of said cathode active material is adapted to store said absorbedoxygen.
 41. The fuel cell according to claim 40, wherein saidelectrolyte solution contacting surface is adapted to react said storedoxygen with an electrolyte solution.
 42. The fuel cell according toclaim 1, wherein said oxygen electrode comprises a gas diffusion layer,a catalyst layer, a polytetrafluoroethylene layer, and a currentcollector grid.
 43. The fuel cell according to claim 42, wherein saidcatalyst layer is disposed between said gas diffusion layer and saidcurrent collector grid.
 44. The fuel cell according to claim 42, whereinsaid gas diffusion layer is disposed between said catalyst layer andsaid polytetrafluoroethylene layer.
 45. The fuel cell according to claim42, wherein said polytetrafluoroethylene layer is in intimate contactwith said oxygen containing stream.
 46. The fuel cell according to claim42, wherein said catalyst layer is dispersed throughout said currentcollector grid.
 47. The fuel cell according to claim 42, wherein saidcurrent collector grid is in intimate contact with said electrolytestream.
 48. The fuel cell according to claim 42, wherein said currentcollector comprises at least one selected from the group consisting ofmesh, grid, matte, expanded metal, foil, foam and plate.
 49. The fuelcell according to claim 42, wherein said current collector gridcomprises 40 wires per inch running horizontally and 20 wires per inchrunning vertically.
 50. The fuel cell according to claim 42, whereinsaid current collector grid is comprised of a conductive metal.
 51. Thefuel cell according to claim 42, wherein said current collector grid iscomprised of nickel.
 52. The fuel cell according to claim 42, whereinsaid gas diffusion layer has the following composition: 40 weightpercent polytetrafluoroethylene; 60 weight percent carbon black.
 53. Thefuel cell according to claim 42, wherein said catalyst layer has thefollowing composition: 50 weight percent of a mixture by weight of 40percent polytetrafluoroethylene and 60 percent carbon black, 15 weightpercent carbon black; 15 weight percent graphite; 20 weight percentsilver oxide.
 54. The fuel cell according to claim 53, wherein saidsilver oxide includes a lithium aluminum alloy.
 55. The fuel cellaccording to claim 53, wherein said silver oxide includes gallium. 56.The fuel cell according to claim 1, wherein said electrolyte solution iscomprised of a potassium hydroxide solution.
 57. The fuel cell accordingto claim 1, wherein said oxygen containing stream comprises air.
 58. Thefuel cell according to claim 1, wherein said hydrogen stream comprisesgaseous hydrogen.